Carboxylic acids are useful feedstocks for the production of alkenyl carboxylates. Thus, for example, acetic acid is used to manufacture vinyl acetate. Acetic acid may be produced by the catalytic oxidation of ethylene and/or ethane. Water is produced as a by-product of the oxidation process. In addition, water (steam) is generally added to the feedstock to improve selectivity to acetic acid.
Vinyl acetate is generally prepared commercially by contacting ethylene and acetic acid with molecular oxygen in the presence of a catalyst active for the production of vinyl acetate. Water is produced as a by-product of the reaction.
The water produced as a by-product and additionally any added water in the afore-mentioned processes must be removed from the product acid and alkenyl carboxylate, necessitating expensive capital expenditure and operating costs.
Integrated processes for producing acetic acid and/or vinyl acetate are known in the art. EP-A-0 877 727 discloses an integrated process for the production of acetic acid and/or vinyl acetate from a gaseous feedstock comprising ethylene and/or ethane. The integrated process comprises a first step wherein ethylene and/or ethane is catalytically oxidised in a first reaction zone to produce a product stream comprising acetic acid and water. The acetic acid stream may be passed directly to a second reaction zone without prior removal of water and contacted therein with a molecular oxygen-containing gas in the presence of a catalyst to produce a second product stream comprising vinyl acetate and water.
Research Disclosure 2244 of 1992 (June) No. 338 describes a process for the oxidation of ethane and/or ethylene to produce acetic acid in which the by-product carbon monoxide is oxidised to carbon dioxide. According to this document, the acetic acid, unreacted ethane (if present) and ethylene is passed with or without carbon dioxide and water removal, to a reactor having a suitable catalyst for the production of ethyl acetate or, with the addition of oxygen, for the production of vinyl acetate.
It is also known from, for example, EP-A-0 985 656 that the introduction of water into a reactor for producing vinyl acetate can adversely affect the selectivity to vinyl acetate product. Thus, in EP-A-0 985 656 which discloses a process for the manufacture of vinyl acetate by combining ethylene, acetic acid and an oxygen-containing gas at elevated temperature in the presence of a catalyst, the liquid by-product stream comprising acetic acid and water is treated to reduce the water content thereof before being recycled to the reactor.
Thus there remains a need for an improved integrated process for the manufacture of an alkenyl carboxylate such as vinyl acetate.
In particular, it would be desirable, if in an integrated process for the production of an alkenyl carboxylate by the oxidation of a C2 to C4 alkane to produce the corresponding alkene and carboxylic acid and wherein the alkene and carboxylic acid are contacted with a molecular oxygen-containing gas to produce the alkenyl carboxylate, to minimise the number of water removal processing steps without adversely affecting the selectivity to alkenyl carboxylate, such as vinyl acetate.